1. Field of the Invention
The present invention relates to the preparation of flexible polyurethane foams having improved physical properties by the reaction of polymer polyls with polyiscoyanates. More particularly, this invention relates to the preparation of flexible polyurethane foams particularly useful as carpet underlays and padding.
2. Description of the Prior Art
Polyurethane foams generally are prepared by reacting an active hydrogen-containing compound, as determined by the Zerewitinoff method, and a polyisocyanate in the presence of a blowing agent, a reaction catalyst and a foam stabilizer. The most common active hydrogen-containing compounds contain predominantly hydroxyl groups and include polyesters and polyethers. It is widely recognized in the art that the preparation of commercially useful polyurethane foams requires carefully balancing a large number of factors including inter alia the selection of primary reactants and reaction conditions, catalyst selection, and the surfactant employed.
The prior art has described many attempts to improve particular properties of flexible polyurethane foams, e.g., foam density, firmness, etc., without significantly impairing other desirable characteristics so as to produce foams suitable for particular applications. In one approach, various inert filler materials are blended into the foaming mixture during polymerization. While such modifiers can successfully increase foam density, and at times improve foam firmness, such additives generally lead to a deterioration in other important foam properties. In particular, dynamic properties such as durability generally are unavoidably impaired and the life of the foam under dyanmic use is reduced greatly. Consequently, filled flexible foams typically have been limited to specialty products.
In another approach, exemplified by U.S. Pat. No. 3,506,600, a densified, flexible polyurethane foam is prepared by passing a partially cured cellular foam material through the nip of opposing pressure rollers. This approach not only adds to processing costs, but also creates a large density gradient across the vertical section of the densified foam. Such a gradient is udesirable since it results in the production of unnecessary and often useless by-product material.
Most recently, improved polyol precursors have been developed which can be used to produce flexible polyurethane foams having enhanced load bearing resiliency. These polymer/polyols or graft polyols are prepared by the in situ polymerization of ethyleneically unsaturated monomers in an appropriate polyol in the presence of a free radical catalyst. When used as the starting polyol reactant in the preparation of flexible foams, these polymer/polyols commonly are mixed with conventional polyether polyols to optimize product characteristics, reduce cost, and make the polyol component easier to handle. Otherwise, these polymer/polyols tends to degrade certain characteristics such as tear, tensile and elongation properties and fire retardancy evident in less firm flexible foams.
The prior art has also disclosed that the cellular structure of polyurethane foams prepared by the reaction of a polyisocyanate with a polyester and/or a polyether polyol can be modified to an open, non-uniform cellular structure resembling a natural sponge by adding filled or unfilled diorganosilicone oil to the reactant mixture. Filled diorganosilicone oils have not been used, however, specifically to improve the load bearing resiliency of flexible polyurethane foams, particularly foams prepared by reacting a high solids polymer/polyol with a polyisocyanate.
It is therefore an object of the present invention to provide a method for preparing a flexible polyurethane foam having excellent firmness.
It is another object of this invention to provide a method for preparing a firm, flexible polyurethane foam without impairing the cushioning characteristics of the foam.
It is a further object of the present invention to provide a method for preparing a flexible polyurethane foam having exellent physical properties that does not require post-formation processing steps.
It is still another object of this invention to provide a method for controllably altering the cellular structure of a flexible polyurethane foam so as to improve its load bearing resiliency.
Still a further object of the present invention is to provide a modified polyurethane foam having improved resilience characteristics making it ideally suited for use as a carpet underlay or padding.
These and other objects, advantages and features will be apparent to those skilled in the art from the following disclosure and appended claims.